In recent years, depletion of oil resources and global reduction of the amounts of carbon dioxide gas generated have been the subjects of dispute. Rising oil prices are predicted in the future and thus the development of alternative materials to petroleum has been required. For example, one such attempt has already been launched, involving the bioconversion of biomass, sugar, starch, fat and oil, proteins, and the like produced by plants from water and carbon dioxide gas via solar power so as to use the resultants as alternative materials to petroleum. For example, technology for producing plant-derived polylactic acid or polybutylene succinate as an alternative material to plastic produced using petroleum has been under development. Moreover, in the United States, Brazil, and the like, ethanol is produced via fermentative production from sugar, starch, or the like, blended with vehicle fuel purified from petroleum, and then used.
Furthermore, examples of chemical products that are important as resin raw-materials for industrial solvents such as paint and ink include acetone and isopropanol (which is synonymous with the term “2-propanol”). Isopropanol has been conventionally synthesized using petroleum as a raw material. However, isopropanol synthesis from biomass via fermentation processes is desired because of problems that include the depletion of petroleum and CO2 reduction in air. Conventionally, it is known that Clostridium acetobutylicum conducts fermentative production of acetone and isopropanol together with butanol (Non-patent Document 1: Biotechnology, 2nd ed., vol. 1, pp. 285-323, 1993). It is also known that acetone is synthesized through introduction of a Clostridium-acetobutylicum-derived acetone synthesis gene into Escherichia coli (Non-patent Document 2: Appl. Environ. Microbiol., 73, 1079-1085, 1998; Patent Document 1: US2009/293125; Patent Document 2: WO 2009/008377; Patent Document 3: WO 2009/028582).
An example has been reported, whereby isopropanol is synthesized with the use of Escherichia coli into which an isopropanol dehydrogenase gene has been introduced in addition to a Clostridium-acetobutylicum-derived acetone synthesis gene (Non-patent Document 3: Appl. Environ. Microbiol., 64, 7814-7818, 2007). However, bacteria including Escherichia coli are problematic due to their low resistance to organic solvents. Several methods for solving this problem are known. However, the resulting resistance is insufficient for industrial production of organic solvents (Patent Document 4: WO 2007/146377; Patent Document 5: WO 2007/130560; Patent Document 6: WO 2008/073406; Patent Document 7: U.S. Pat. No. 6,156,532). Specifically, bacteria such as Escherichia coli are problematic due to their weak cell membranes against organic solvents. Hence, bacteria are thought to be ineffective for production of organic solvents. On the other hand, yeast is highly resistant to organic solvents, but no example of the production of an organic solvent (e.g., isopropanol or acetone) through the introduction of a gene into yeast has been reported.